It was the summer of 2003 and I was being followed around by a Finnish TV crew making a documentary about me. When they asked me to demonstrate my method, I took them to a place near Helsinki called Lauttasaari, right on the sea. I knew it had a great horizon.

The weather was so weird. It was seven in the evening in July. The air was warm, the sun was low, and the biggest thunderstorm of the summer was about to break. Looking out, I got so excited. "Excuse me," I said. "I can't let the opportunity go – I have to do something real." So I took off my clothes and set up this shot.

Normally I work alone, photographing myself using a cable release. But it wasn't long enough so I had to ask one of the crew to press the shutter. Thankfully, he timed it right and got the wave breaking on the rock. It was difficult, though: he didn't know how to wind the film on, and I had to keep rushing back to the camera, 20 metres away over slippery rocks. And the rain was just about to start, so we were in a real hurry.

What makes this picture is that rare, unimaginable light. I use a medium format camera and printed this picture straight from the negative. But every time I exhibit it, people think I used extra lights, or Photoshopped it. But it's absolutely straight.

I do a lot of nude studies. There's nothing sexual or pornographic in this. Some people have seen it as an allusion to the Little Mermaid sculpture in Copenhagen, but I had no specific work in mind. Sitting on the rock was just the simplest way for me to be in the picture.

CV

Born: Helsinki, 1972.

Studied: Masters in photography, University of Art and Design, in Helsinki.

Influences: None.

High point: Being awarded the Finnish state prize for photography in 2009. A real honour.

Top tip: Work very hard. You are the caretaker of your work. You have to make sure you do it as well as possible.